The SPIE short course “Introduction to Optical Alignment Techniques” has been taught for over twenty years at many SPIE conferences. It has always been one of the well attended ones, indicating a need for the subject matter. Reviews of first order concepts, and the basic optical aberrations set the stage for understanding how optical systems become misaligned, how to recognize the aberration type and diagnose what is wrong. This will suggest solutions to the alignment problem, enabling failing optical assemblies to be corrected. The course closes with a discussion of the alignment issues that impact off-axis parabolas and higher-order aspheres.
In the design of optical assemblies, emphasis is placed on tolerancing the surface irregularity, which is a driving factor in price and manufacturing prices and time during polishing. Quite often, the default irregularity tolerance in modeling software is assumed to be a 50:50 split between astigmatism and 3rd order spherical aberration (i.e. symmetric zonal errors). In this paper, we reviewed the irregularity of over 1,000 custom fabrication optical surfaces. We looked at the relationship between the spherical and astigmatism aberrations and found generally that a surface will be either astigmatic or spherical, but rarely a mixture of the two. We also looked at the PV and rms of the surfaces and how that compares to the model and the general knowledge. One striking result of our analysis came from a closer analysis of how the optical modeling software package handles ‘power’ errors in the irregularity tolerance. It is possible that there is a mismatch between the model and the optical manufacturer.
The Hyperspectral Polarimetric Imaging (HPI) Testbed system combines a dual-band hyperspectral imager (VNIR and SWIR), a 3-axis polarimetric imager, and a high resolution panchromatic imager. All imagers operate through a common fore-optic, and thus have identical fields of view, with simultaneous image capture. The HPI testbed system was developed to aid a sentry in the surveillance of broad sectors for intrusion by ground vehicles or other non-natural objects. The various image components are readily combined through image fusion, which lends itself well to anomaly detection algorithms. This paper describes the general HPI testbed system design and performance, and also provides a detailed description of the polarimetric imaging system, calibration methods, and performance.
Recent advances in axial gradient material fabrication via the diffusion of glass plates has opened the door to a wide variety of optical design applications incorporating entire lenses of gradient index material. A proprietary software-driven process developed at LightPath Technologies Inc. creates gradient index glass by fusing together a stack of discrete glass plates, where each constituent plate has a distinctive composition and desired optical properties. LightPath's ability to prescribe large optical index changes (up to 0.47) throughout a glass substrate of virtually any diameter and thickness (macro gradient), invokes an interesting question: what are the properties of a solid gradient index lens and how can these properties be used most efficiently and effectively? This paper reports on a parametric study of third order spherical aberration vs. shape factor, for a macro gradient F/3 singlet lens whose index varies by +/- 0.4 in linear, quadratic and cubic profiles.
A 20 power (20X) all-reflective microlithography objective has been fabricated for use in the soft x-ray region at a wavelength of 13 nm. The design uses the Schwarzschild configuration where two spherical mirrors form a point image from a point object. The centers of curvature of the two mirrors in such a system are coincident. However, to increase field of view, fifth- order spherical must be balanced by third-order spherical. This is accomplished by separating the two curvature centers longitudinally. Lateral separations quickly introduce coma into the wavefront. Holding the curvature center positions rigidly in place relative to the object and image positions is required for maintaining the wavefront quality. Suitable x-ray sources are not common; therefore, the rigidity must also be viewed as a level of ruggedness suitable for transportation from the assembly facility to the test facility. In this paper we share the techniques that we have used to satisfy the requirements of MTF, wavefront quality, ease of alignment, and ruggedness.
SC010: Introduction to Optical Alignment Techniques
This course discusses the equipment, techniques, tricks, and skills necessary to align optical systems and devices. You learn to identify errors in an optical system, and how to align lens systems.